This invention relates to apparatus for controlling the injection, into a well tubing string, of fluid such as gas for gas lift operations or liquids containing treatment chemicals; and more particularly to side pocket mandrels and flow control devices in the side pocket receptacles of such mandrels.
Side pocket mandrels have been used for many years for different applications involving the flow of fluids from the exterior of a tubing string into the interior thereof. Such applications include the practice of gas lift techniques for recovery of oil from oil wells, and the injection of liquids which may include treatment chemicals for different treatment purposes within the well. Davis et al U.S. Pat. No. 4,066,128, issued Jan. 3, 1978, is concerned with a side pocket mandrel including a flow control device in the side pocket receptacle thereof for controlling the injection of gas into the tubing string for a gas lift operation. The flow control device of this Davis patent includes a sliding sleeve valve which controls the port opening into the side pocket receptacle from the exterior of the mandrel, and which is shiftable between a port-closing and a port-opening position. This sliding sleeve valve is operated automatically by a flow control valve which is inserted selectively into the side pocket receptacle of the mandrel. When the control valve is placed therein, the sleeve valve is moved automatically to the port-opening position; and when the control valve is removed from the receptacle, the sliding sleeve valve is moved automatically to the port-closing position.
A disadvantage of the flow control device of the Davis patent is that the sliding sleeve valve is not removable from the side pocket receptacle. Accordingly, with this design, should the sliding sleeve valve become defective and require servicing or replacement, it will be necessary to shut down the well and withdraw from the well the side pocket mandrel carrying that sliding sleeve valve and of course all of the associated production tubing string. This is obviously a time consuming and expensive procedure, and a much preferred form of flow control device would include a sliding sleeve valve which could be removed from the side pocket receptacle either for servicing or replacement.